SS2 Chemistry Lesson Note on Halogens

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TOPIC: HALOGENS

CONTENT:

1. ELECTRONIC CONFIGURATION OF HALOGENS, PHYSICAL PROPERTIES OF HALOGENS, AND GRADATION DOWN THE GROUP.
2. CHEMICAL PROPERTIES OF HALOGENS AND GRADATION DOWN THE GROUP
3. USES OF HALOGENS AND THEIR COMPOUNDS.

PERIODS 1 AND 2: ELECTRONIC CONFIGURATION OF HALOGENS

Halogens are found in group (viii) of the periodic table and consist of fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I) and Astatine (At),.

The name halogen is of Greek origin meaning salt formers because they readily form salts from metals. Halogens are very reactive non- metals with remarkable similarities in properties. This is because each halogen atom has seven only one electron to attain the octet. They are strong oxidizing agents with varying oxidation Numbers. The halogens are highly electro negative elements. The halogens share electrons to form covalent compounds or accept electrons to form ionic compounds. It is the electronic configuration of halogens that accounts for their electronegative nature, oxidising ability and the fact that they form mainly single covalent bonds.

ELECTRO CONFIGURATION AND SOME PROPERTIES OF THE HALOGENS AND GRADATION OF THE PROPERTIES

Element	Atomic Number	Electronic configuration	Atomic radius	Ionic radius	Electro-negativity	Electro-affinity	Atomic Mass
Fluorine [F]	9	[2,7] IS22S22P5	0.072	0.136	4.0	-3.35	19.0
Chlorine [Cl]	17	[2,8,7] IS22S2 2p63S23P5	-0.099	0.181	3.0	-3.61	35.5
Bromine [Br]	35	(2,8,18,7) ..3S23P63d104S2	-0.114	0.195	2.8	-3.36	80.0
Iodine [I]	53	(2,8,18,18,7) ….4S24P64d10	0.133	0.216	2.5	-3.06	126.9
Astatine [At]	85	(2,8,18,32,18,7)  ..5S25P65d106S26P5	—-	—-	2.2	—-	210

PHYSICAL PROPERTIES OF THE HALOGENS

Element	Fluorine[F]	Chlorine[Cl]	Bromine [Br]	Iodine[I]
Atomic number	9	17	35	53
Relative Atomic Mass	19	25.5	79.9	126.9
Physical state at 20	Gas	Gas	Liquid	Solid
Colour	Pale yellow	Greenish yellow	Dark-red	Black
Density(g/cm3)	——	1.9	3.2	4.9
Melting point ( ). Boiling point (	-220	-101	-7	113
Solubility in water (g per 100g of water)	Reacts readily with water	0.59	3.6	0.018

EVALUATION

1. What is the atomic number of chlorine?
2. With the knowledge of atomic number, draw the electronic configuration of chlorine.
3. What is the colour of chlorine gas?

PERIOD 3: CHEMICAL PROPERTIES AND GRADATION DOWN THE GROUP

The chemical reactivity of the halogens decreases down the group from fluorine to iodine. The halogens are good oxidising agents and their oxidising power decreases from fluorine to iodine. The halogens try to attain the stable noble gas configuration either by sharing electrons or by accepting electrons. The following reactions illustrate the reactivity trend among the halogens.

1. Halogens can react with metals as shown in the equations below

2Na_(s) + F_{2(g)  →} 2NaF_(s)

2. Halogens react with non-metals as shown below

C_(s) + 2F_{2(g) →}  CF_4(s)

Xe+ 2F  _→   XeF_4(s)

P_4(s) + 6I_{2(s)  →} 4PI_3(s)

P_4(s) + 6Cl_{2(g)   →}     4PCl_2(s)

P_4(s) + 10Cl_{2(g)    →}    4PCl_5(s)

H_2(g) + F_{2(g)    →}    2HF_(g)

H_2(g) + Cl_{2(g)   →}   2HC_l(g)

Br_2(g) + H_{2(g)   →}     2HBr_(g)

I_2(g) + H_{2(g)    →}    2HI_(g)

The order of reacting is F₂> Cl₂>Br₂>I₂. The acid strength of the hydrogen halides follow the order:

HI>HBr>HCl>HF

The stability of Hydrogen halides decreases from chlorine to iodine: HCl>HBr>HI.

Chlorine is now an electron acceptor and so are other halogens and in so doing acts as oxidising agents.

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